Information
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Patent Grant
-
6434822
-
Patent Number
6,434,822
-
Date Filed
Wednesday, September 13, 200024 years ago
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Date Issued
Tuesday, August 20, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
- Echols; P. W.
- Compton; Eric
Agents
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CPC
-
US Classifications
Field of Search
US
- 029 434
- 029 890142
- 029 88841
- 029 890124
- 123 472
- 239 5339
- 239 584
- 239 900
- 219 12113
- 219 12163
- 228 1246
- 251 12918
- 251 12921
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International Classifications
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Abstract
A method of assembly of a fuel injector having a valve plunger reciprocable in a guide tube for movement from a closed position engaging a valve seat to an open position engaging a valve stop by energizing of a solenoid coil to move the plunger against a biasing spring, wherein the method includes setting the valve stop at a position effective to establish the desired valve stroke, and fixing the valve stop to the guide tube by first laser spot welding the valve stop in the guide tube to fix the position of the valve stop without changing the set gap, and then laser seam welding the valve stop in the guide tube at an axial location beyond the spot welds, relative to a plunger-engagable end of the valve stop, to provide a hermetic seal around the valve stop.
Description
TECHNICAL FIELD
This invention relates to solenoid actuated fuel injectors for engines and the like and, in particular, to a method of assembly that simplifies setting of the injector valve stroke.
BACKGROUND OF THE INVENTION
A solenoid actuated fuel injector for automotive engines is required to operate with a small and precise stroke of its core or valve in order to provide a fuel flow rate within an established tolerance. In some current injectors, the stroke is adjusted at assembly by moving an adjustable valve seat a predetermined dimension from a valve seated position. This adjustment is made after sealing of joints in the fuel conducting elements has been performed, such as by crimping or penetration welding of a solenoid pole piece to a surrounding tubular valve guide. This allows the stroke setting operation to compensate for component movement or shrinkage, which are likely occurrences with crimped or welded joints. However, the requirement for an adjustable valve seat adds cost and complexity to the assembly process.
SUMMARY OF THE INVENTION
The present invention provides a pole piece or core stop that is welded to a guide tube after a stroke setting operation. A continuous penetration seam weld is used in order to provide a hermetic seal of the joint between the parts. The hermetic penetration seam weld does not tend to move the parts axially, or normal to the direction of weld penetration. However, such a seam weld does tend to shrink the outer tubular component, which can cause a shift in the preset valve stroke.
In accordance with the present invention, the stroke is set by adjusting the position of the pole piece or valve stop within an associated guide tube to obtain the desired valve stroke. The guide tube is then fixed to the valve stop in a manner that maintains the preset valve stroke. This is accomplished by first welding the guide tube to the pole piece or valve stop by a series of penetration spot welds. These secure the components together without causing any change in the valve stroke setting, since the non-melted portions of the guide tube between the spot welds prevent dimensional change and absorb the shrinkage stresses. Thereafter, a continuous hermetic seam weld is made between the parts at a point axially spaced from the spot welds in a direction away from the valve seat. The spot welds then maintain the relative dimensions of the components between the spot welds and the valve seat so that any shrinkage in the assembly due to the seam weld occurs in the components away from the valve seat and has no effect upon the preset valve stroke.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1
is a cross-sectional view of a fuel injector including components assembled by a method according to the invention;
FIG. 2
is a schematic view illustrating brazing of the guide tube into the valve body;
FIG. 3
is a schematic view illustrating welding of the seat support to the valve body;
FIG. 4
is a schematic view illustrating setting of the valve plunger and tubular pole at a zero lift position in the guide tube;
FIG. 5
is a schematic view illustrating raising of the pole in the guide tube by the distance of the desired valve stroke;
FIG. 5A
is a fragmentary cross-sectional view showing an alternative method of setting the tubular pole for the desired valve stroke;
FIG. 6
is a schematic view illustrating laser spot welding of the guide tube to the tubular pole; and
FIG. 7
is a schematic view illustrating laser seam welding of the guide tube to the pole upward of the spot welds.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to
FIG. 1
of the drawings in detail, numeral
10
generally indicates an exemplary solenoid actuated fuel injector for an engine. Injector
10
includes a non-magnetic cover
12
enclosing a solenoid coil
14
. A fuel tube extends through the coil and acts as a tubular magnetic pole
16
. An outer strap
17
connects with the inner pole
16
, extends around the coil
14
and connects with an annular member forming a valve body
18
. A non-magnetic (e.g. stainless steel) guide tube
20
extends upward from the valve body
18
and surrounds the lower end of the magnetic pole
16
to provide an initially telescoping joint
21
that is subsequently sealed by welding as will be subsequently described. A guide ring
22
is spaced below the guide tube
20
in a central bore
24
of the body
18
.
A seat support
26
is fixed to a lower end of the valve body
18
. The seat support carries a seat member
28
that combines the functions of a valve seat and a director plate. The valve body
18
is fixed, as by welding, to the seat support
26
and engages outer edges of the seat support to position the support and provide a fuel seal. The central bore
24
of the valve body encloses a reciprocable valve plunger
30
that is guided in the bore by the guide tube
20
and the guide ring
22
. The plunger is a hollow member with a lower end
32
having a central opening
34
and side openings
36
adjacent the end. A plunger spring
38
biases the plunger downward against annular seat rings
40
that form a valve seat on seat member
28
. Spray holes
42
are spaced between the rings
40
and direct a fuel spray out through an open center
44
of the seat support
26
when the valve plunger is lifted off the seat rings
40
. A filter supporting calibration ring
45
is pressed into the tubular pole
16
for maintaining a calibrated compression force on the plunger
30
through the spring
38
and for filtering fuel entering the injector.
The plunger
30
is guided by the guide ring
22
and the guide tube
20
, which are both fixed in cylindrical counterbores around the central bore
24
of the valve body
18
. The counterbore in which the guide tube is fixed lies adjacent a cylindrical inner recess
46
that may receive a ring of brazing material during assembly of the injector.
The guide tube
20
and the tubular pole
16
define a fuel passage
48
for conducting pressurized fuel in the injector. Thus, the cylindrical joint
21
between the guide tube
20
and the pole
16
must be hermetically sealed to prevent fuel leakage as well as structurally strong to maintain the set position of the magnetic pole or valve stop
16
. In accordance with the invention, the joint
21
is secured by laser seam welding of the tube
20
to the pole
16
in a manner to be subsequently described. However, it is first necessary to partially assemble the injector components and to set the valve stroke prior to the welding steps in order to obtain the desired advantage of maintaining a preset valve stroke without the need for subsequent adjustment.
Alternative methods of assembly and calibration are possible and any suitable manner of setting the valve stroke may be used. In a preferred method, illustrated in
FIGS. 2-7
, the guide tube
20
is fixed in the valve body
18
by any suitable process, such as welding or furnace brazing the components together at the recess
46
as shown in FIG.
2
. The actual valve seat member
28
and seat support
26
for the injector are also fixed in their final positions in the valve body
18
by laser welding the seat support
26
to the valve body
18
as shown at
49
in FIG.
3
. As illustrated in
FIG. 4
, the valve plunger
30
is then installed in the guide tube
20
and the valve stop or magnetic pole
16
is inserted into the guide tube and urged downward, as by a spring loaded fixture, not shown, against the plunger
30
, forcing the plunger lower end
32
against the valve seat rings
40
. The valve stroke is thus effectively set to zero.
As shown in
FIG. 5
, by any suitable means, the magnetic pole or valve stop
16
is then forced upward in the guide tube
20
the exact dimension of the desired valve stroke so that the tubular magnetic pole
16
is then set in position to provide the desired valve stroke. The stroke length is very small, on the order of 95 microns, so accuracy in the stroke setting is important. Using the actual injector parts in their installed positions eliminates any effect from parts tolerances, because the stroke is set exactly equal to the upward movement of the pole
16
.
Various alternative methods might be used for raising the valve stop (pole
16
) to set the valve stroke. With the illustrated embodiment installed in an assembly fixture, the upper end of the tubular pole
16
could be gripped by an adjusting device
50
, as shown, to raise the pole
16
a dimension equal to the valve stroke. In other embodiments of injectors which have an opening through the valve seat, an adjusting device may be inserted through the seat opening to engage the lower end of the valve plunger and push both the plunger
30
and the pole
16
upward to the desired position of the pole.
In another alternative for the present embodiment, shown in
FIG. 5A
, the installation of the valve seat member
28
and seat support
26
may be omitted until after the stroke setting steps. Instead a fixture
52
may be inserted in place of the valve seat and support as shown in FIG.
5
A. The fixture
52
would seat against flat seat mounting surface
54
of the body
18
and would include a central protrusion
56
having the height of the desired valve stroke. Then, the plunger
30
would engage the protrusion
56
upon its insertion into the guide tube
20
with the tubular pole
16
engaging the plunger
20
(as shown in FIG.
4
). This would locate the pole
16
at the position desired for setting the valve stroke so further movement of the pole would not be required.
At this point, regardless of by what method the desired stroke has been established, the magnetic pole
16
is now in position to be fixed to the guide tube
20
. Securing the parts with a laser seam weld would be effective in sealing the cylindrical joint
21
between the pole
16
and tube
20
against the leakage of fuel therethrough from the fuel passage
48
. However, such a penetration weld has been found to cause axial shrinkage of the guide tube member, which causes a change in the preset valve stroke. To avoid this, the present invention provides a novel two step welding process that fixes the parts together without changing the stroke while also providing the required hermetic sealing of the joint
21
.
As shown in
FIGS. 5 and 6
, the guide tube
20
is first fixed to the tubular pole
16
by a plurality of circumferentially spaced laser spot welds
58
located toward the lower end of the valve stop formed by the tubular pole
16
. This process does not change the preset valve stroke, since the unmelted portions of the guide tube
20
between the spot welds
58
maintain their axial dimensions and hold constant the axial position of the valve stop lower end.
In the second step, shown in
FIG. 7
, the guide tube
20
is fixed to the tubular pole
16
by a penetration laser seam weld
60
through the guide tube
20
above the location of the spot welds
58
, that is, at an axial location beyond the spot welds relative to the plunger-engagable end of the valve stop (tubular pole
16
). The seam weld
60
provides the hermetic seal of the joint
21
between the pole
16
and guide tube
20
. Any axial shrinkage of the guide tube due to the seam welding occurs above the seam weld
60
, since the lower portion of the guide tube
20
is axially fixed by the prior spot welds
58
.
Thereafter, the partially assembled injector, with its established valve stroke, may be completed by assembling the remaining components. This includes installing the coil
14
and the surrounding outer strap
17
, which may be welded to the pole
16
and the valve body
18
. The plastic cover
12
is also placed in position and a lock ring, not shown, is snapped onto the pole
16
, which also serves as the fuel inlet tube for the injector. Within the fuel passage
48
, the plunger spring
38
is installed with the calibration ring
45
that is pressed into the pole
16
to maintain a desired spring load and which also carries a fuel inlet filter
62
, all as is shown in FIG.
1
.
As a result, the initial preset valve stroke is maintained during the subsequent welding of the guide tube
20
to the pole
16
, providing a hermetic seal while avoiding any need for subsequent adjustment of the valve stroke in final assembly of the injector.
While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.
Claims
- 1. A method of assembly of a fuel injector having a valve plunger reciprocable in a guide tube for movement from a closed position engaging a valve seat to an open position engaging a valve stop by energizing of a solenoid coil to move the plunger against a biasing spring, said method comprising:installing the plunger in the guide tube in engagement with one of the valve seat and a reference member; installing the valve stop in the guide tube and setting a predetermined gap between the valve stop and the normally closed position of the plunger to establish a desired valve stroke; laser spot welding the valve stop in the guide tube to maintain the set gap; and laser seam welding the valve stop in the guide tube at an axial location beyond the spot welds, relative to a plunger-engagable end of the valve stop, to provide a hermetic seal around the valve stop.
- 2. A method as in claim 1 wherein the actual valve seat for the injector is fixed to an injector body supporting the guide tube and the valve stroke is set relative to a portion of the valve seat engagable by the plunger.
- 3. A method as in claim 2 wherein the valve stop is installed in engagement with the plunger as the plunger engages the valve seat and the valve stop is then moved away from the valve seat a dimension equal to the desired valve stroke.
- 4. A method as in claim 3 wherein the valve stop is moved said dimension by forcing the plunger away from the valve seat while the plunger remains in engagement with the valve stop.
- 5. A method as in claim 1 wherein a reference member is installed temporarily in place of the valve seat and the valve stroke is set relative to a portion of the reference member engagable by the plunger.
- 6. A method as in claim 5 wherein the reference member is mounted in place of the valve seat and has a plunger engagable portion protruding beyond the normal position of the valve seat by the dimension of the desired valve stroke, whereby engagement of the plunger with the reference member and the valve stop with the plunger positions the valve stop at the desired position.
US Referenced Citations (9)